This section is from the book "Soyer's Standard Cookery", by Nicolas Soyer. Also available from Amazon: Soyer's Standard Cookery.
Put into a saucepan one and one-half pints of clear poultry-stock and one gill of mushroom cooking liquor. Reduce to two-thirds; add one pint of "poultry veloute"; reduce again, stirring with a spatula the while, and combine half pint of cream with the sauce, this last being added by degrees.
When the sauce has reached the desired consistence, strain through a sieve, and add another gill of cream and two ounces of best butter. Stir with a spoon, from time to time.
 
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